The surface smoothness of exterior body panels is an important consideration in the automotive industry. In order to study changes in the surface quality of these exterior body panels resulting from new material formulation and processing techniques, and for quality control in the plant production area, it is necessary to have a fast and accurate inspection which provides easy-to-interpret results.
Prior art methods accomplish surface inspection by examining one or more line profiles or images reflected off the surface under inspection. Generally, they fail to thoroughly inspect the entire surface during a single examination. Such line profiling or imaging apparatus and methods which provide discrete rather than continuous or full-field surface information include the back-lighted grid method, green-room inspection and laser beam traces. Mechanical profiling of the type carried out with a stylus similarly provide discrete rather than full-field results.
The closest known prior art is disclosed in Breske, U.S. Pat. No. 3,439,988, which discloses an apparatus for inspecting a reflective surface, comprising a slide projector for projecting one or more light or dark lines onto the reflective surface under inspection, and a screen positioned for intercepting the reflected light rays and displaying the line image. The Breske apparatus for surface inspection uses a slide having one or more discrete lines to uncover surface defects. Breske also contemplates illuminating an entire surface to permit an overall inspection of any reflective surface (see column 3, lines 37-42 and column 4, line 1). However, it is important to note that this teaching is made in the context of utilizing a slide projector, wherein the slide projector includes a light source and a lens for focusing an image. The positioning of the light source and lens in a slide projector arrangement effectively makes the Breske light source an extended light source.
In contrast, the present invention uses a point light source, whereby the results achieved by the apparatus and method of the present invention are superior to those which can be realized by the Breske apparatus and method when an entire surface under inspection is illuminated. Moreover, in order for Breske to obtain a sharp image, a fixed distance between the lens and screen must be adhered to for a given lens setting, while in comparison, the screen of the present invention can be positioned within a range of distances from the object under inspection, without adversely affecting the results obtained.